This invention relates generally to the field of gas flow-meter devices and more specifically to an orifice assembly for a gas-metering device.
The invention is especially applicable to precisely calibrated gas-metering orifices for metering a flow of gas, such as therapeutic oxygen, at a prescribed rate to a patient. The invention also relates to a flow meter which uses such metering orifices to selectively provide a plurality of accurate gas flow rates and to a pressure regulator unit having all of its component parts retained therein.
In the past, orifice punch devices have been used to make orifices of various sizes for flow meters. Generally with these punch devices, the operator punches an orifice in an element and then moves the element from the punch device to a separate flow testing device for measurement of the flow therethrough. If a greater rate of flow is required, the element is transferred back to the punch device for further punching. The transfer of the element back and forth for further punching and testing is continued until the orifice is properly sized. Such a procedure is an inefficient use of the operator's time. In the alternative batch process, the operator punches a series of elements to form similar size orifices in each element. Although more time efficient, batch processing often requires greater uniformity of elements than is economically feasible during the manufacturing process.
Another method of providing a volumetric metering or gas flow is described in Messick, U.S. Pat. No. 4,909,476, issued Mar. 20, 1990, the disclosure of which is herein incorporated by reference. Messick describes an orifice assembly that includes a plurality of brass disks. The disks are held in position by an O-ring disposed between the disks and a retaining plate fixed to a rotor. Orifices of a predetermined size are formed in each brass disk to allow passage of pressurized gas at a fixed rate through the brass disks. A piercing fixture accommodating a needle is used to pierce the brass disks. Since the needle is tapered, advancement of the needle through some defined distance creates an orifice of a desired size.
However, provision of brass disks and the method of orifice formation described by Messick has certain practical limitations under industrial conditions. Proper positioning of large numbers of the small brass disks is difficult and time consuming. In addition, over-advancement of the needle of the piercing fixture can result in an improperly sized orifice that must be removed and replaced, a time consuming process.